1. Field of the Invention
The invention relates to an apparatus for chemical treatment of any selected portion of a subterranean well bore by incorporation of an inflatable tool in combination with a compensating chamber valve member.
The invention also relates to a pressure compensating valve mechanism which may be used independent of the inflatable tool.
2. Summary of the Prior Art
Vertically spaced, inflatable packing elements have been widely used to isolate a selected portion of a well bore for chemical treatment. Prior art apparatus for achieved circulation while the treatment apparatus was being run into the well by passing the circulation fluid through the entire tool. See U.S. Pat. No. 4,708,208. Furthermore, the required manipulation of valves in prior art treatment apparatus have generally required the utilization of set down weight. This renders impractical the use of coiled tubing as the fluid supply conduit upon which the treatment apparatus is run into the well, since coiled tubing cannot apply any significant amount of set down weight.
It is also highly desirable that the portion of the well bore to be chemically treated not be saturated with fluids employed to effect the inflation or testing of the inflatable packing elements In prior art inflatable apparatuses, all of such setting and/or testing fluids contained in the coiled tubing were injected into the isolated well bore portion prior to the chemical treatment fluid ever reaching such portion. This, of course, is highly undesirable.
Lastly, prior art well treatment apparatuses embodying a pair of vertically spaced, inflatable elements have not been designed so as to permit circulation during the retrieval of the entire apparatus from the well. There is a definitive need, therefore, for a well treatment apparatus employing axially spaced, inflatable packing elements that can be run into the well on an auxiliary tool, such as coiled tubing inserted through a pre-existing tubing string and is capable of performing all of the desirable functions, such as circulation during run-in, testing of the tool's pressure integrity after inflation of the packing elements, removal of the inflation and/or testing fluid from the tubing by forcing such fluid into a well bore above the uppermost inflatable element prior to initiating the introduction of chemical treatment fluid into the isolated portion of the well bore, deflation without set down weight to permit the inflatable packing elements to be repeatedly repositioned in the well bore, and lastly, provision for circulating while retrieving the treatment apparatus from the well bore.
A pressure compensating chamber within a pressure compensating valving member will expand as the bias of a spring is overcome to compress the spring resulting in the expansion of the chamber corresponding to the decrease in pressure within the fluid conduit above the apparatus. The pressure compensating member comprises a cylindrical outer housing with a valve housing concentrically movable relative to and within the housing. A fluid flow passageway within the valve housing extends to the top of the well and communicates with the interior of the tool therebelow. Valve head and seat means, preferably provided in series, are carried by the valve housing for selective blocking of fluid flow in one direction through the passageway when the valve head and seat means are in a first relative position and permit fluid flow in one direction through the valve housing when the valve head and seat means are in a second relative position. A pressure chamber is within the outer housing and extends to the lowermost side of the valve head means. A biasing means is provided for biasing the valve housing to contract the pressure chamber, with a biasing means being energized by a decrease of pressure within the fluid conduit thereabove permitting the valve housing to be moved relative to the outer housing to expand the pressure chamber without movement of the valve head means relative to the valve seat means.
In co-pending application Ser. No. 345,343, filed Apr. 28, 1989, entitled "Method and Apparatus for Chemical Treatment of Subterranean Well Bores" and assigned to the same assignee as the present application, there is disclosed a unique inflatable apparatus having particular utility for chemical treatment of subterranean wells. In such device, when the inflatable elements are retracted from set position, the pressured fluid must be exhausted within the apparatus, but such exhaust procedure must be controlled to effectively activate the releasing mechanism. If a back flow valve is utilized with such apparatus, and is mounted, for example, immediately above said apparatus on the conduit carrying the inflatable apparatus, it must not respond to permit fluid flow to the top of the well as a result of the increase in pressure therebelow at any time.
The present invention is directed, in part, to the combination of the apparatus disclosed in that application with a pressure compensating back pressure valving mechanism which provides for an expandable pressure chamber immediately below the lowermost valve head means which may be expanded to compensate for the decrease in pressure of the fluid control conduit during initiation of "deflation" of the inflatable packer elements of the inflatable packer means. While the pressure compensating member of the apparatus has particular utility with that inflatable packer mechanism, the pressure compensating valving member is not necessarily limited to use therewith, and may be used alone and independent of said apparatus in a number of downhole tool applications, or combination with another auxiliary tool in the subterranean well.